Digital multimedia includes video, images and audio data, typically involving a large amount of data. For instance, a twenty-second digitized movie has a data size of 650 Mbytes, and a two hours worth of uncompressed video data would occupy 360 compact disks. Similarly, transmitting a two-hour movie having an uncompressed data format at a rate of 128 kbps would take 169 days.
Video compression has been widely adopted since the advent of digital multimedia technology and the popularization of DVD, web images, mp3 and digital cameras. Several video compression standards have been adopted for a variety of different applications. These include the International Standard Organization (ISO) video compression formats MPEG-1, MPEG-2 and MPEG-4, developed by the Moving Picture Experts Group, and the ITU H.261 and H.263 video standards. These standards came into being at different times when the stage of multimedia technology development had different needs. For example, the MPEG-1 standard supports a 352×240 resolution and an input frame rate of 30 frames per second (fps), and produces video quality slightly below the quality of conventional VCR videos, whereas MPEG-2 supports up to a 1280×720 resolution and an input frame rate of 60 fps and produces video quality sufficient for all major TV standards, including HDTV, with full CD-quality audio. MPEG-2 is also used with DVD-ROM since it has a relatively high compression ratio, defined simply as the ratio of compressed to uncompressed data. The MPEG-4 standard is based on MPEG-1, MPEG-2 technology and is designed to transmit video and images over a narrower bandwidth. MPEG-4 further provides the mixing of video with text, graphics and 2-D and 3-D animation layers. H.261 and H.263 are mainly developed for teleconferencing applications that require both the encoder and decoder operate in real time. H.261 and H.263 have many elements in common with MPEG-1. For H.261, the image dimensions are restricted to two sizes, 352×288 and 176×144. H.263 is based on H.261 but supports more image dimensions.
Each of these conventional standards, including those discussed above, may have its unique application and value. With the advance of the Internet comes the possibility of multimedia over IP networks, wherein the same video data may be desirable for different applications, possibly by different users. Unfortunately, the existing standards for video compression do not allow for inter-convertibility. Hence, one cannot receive an MPEG-2 video stream and convert it into an MPEG-4 stream. Indeed, under the MPEG-4 standard, a video stream may include 2-D and 3-D animations that cannot be included when a video stream is transmitted in MPEG-2 format, by way of example. The inability to build versatility into video transmission may become a serious setback in the future development of broadband communication mega-networks.
On another front of the advancement in multimedia technology, custom-designed hardware devices are replacing generic computing platforms to handle video compression more efficiently. Compression of video data is performed on the fly within the input device such as a PC camera, making real-time video-telephony or video-conferencing a reality. As more hand-held portable devices are equipped to handle multimedia video formats, the video compression hardware is becoming more streamlined by design. Dedicated application specific integrated circuit (ASIC, also referred to as “chip”) and system-on-chip (SoC) applications are being developed. Even so, such chips may not be available for more complex video formats such as MPEG-4, which is usually the desired format for video transmission through the Internet.
The trend towards broadband multimedia transmission requires flexibility in the video format, and the present generation of video chips suffer from the drawback of being able to handle only a single format of video data. Because of the lack of inter-convertibility of the video compression standards, to enable a choice of different output formats from the video intake devices such as a PC camera would require the use of multiple video compression chips, or a “monster” chip with complex and costly circuitry for accommodating the multiple video formats. Such solutions are unattractive solutions as they are both cumbersome and costly.
Accordingly, what is needed is a versatile video compression scheme that enables the dynamic selection of video output formats. The scheme should have sufficient flexibility to allow for the easy implementation of video compression based on all state-of-the-art standards. Also, the scheme must allow the developer to take advantage of the continuous advances in ASIC and SoC technologies which greatly enhance the efficiency and reliability of video transmission.